#include using namespace std; #define rep(i,n) for(int i = 0; i < (int)(n); ++i) #define rrep(i,n) for(int i = (int)(n) - 1; i >= 0; --i) #define ALL(a) a.begin(), a.end() #define Sort(a) sort(a.begin(), a.end()) #define RSort(a) sort(a.rbegin(), a.rend()) typedef long long int ll; typedef long double ld; typedef vector vi; typedef vector vll; typedef vector vc; typedef vector vst; typedef vector vd; typedef pair P; const long long INF = 0x1fffffffffffffff; const long long MOD = 1000000007; const long double PI = acos(-1); template inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; } template inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; } template inline T vin(T& vec, U n) { vec.resize(n); for(int i = 0; i < (int) n; ++i) cin >> vec[i]; return vec; } template inline void vout(T vec, string s = "\n"){ for(auto x : vec) cout << x << s; } template void in(T&... a){ (cin >> ... >> a); } void out(){ cout << '\n'; } template void out(const T& a, const Ts&... b){ cout << a; (cout << ... << (cout << ' ', b)); cout << '\n'; } template void inGraph(vector>& G, U n, U m, bool directed = false){ G.resize(n); for(int i = 0; i < m; i++){ int a, b; cin >> a >> b; a--, b--; G[a].push_back(b); if(!directed) G[b].push_back(a); } } ll n, m; vll h; vector> G; void input(){ in(n, m); vin(h, n); inGraph(G, n, m); } void solve(){ vector> dp1(n + 1, vector(2, -INF)), dp2(n + 1, vector(2, -INF)); dp1[0][0] = 0; dp1[0][1] = 0; dp2[n - 1][0] = 0; dp2[n - 1][1] = 0; rep(i, n){ for(auto x : G[i]){ if(x < i) continue; if(h[i] < h[x]){ chmax(dp1[x][0], dp1[i][1] + h[x] - h[i]); }else{ chmax(dp1[x][1], max(dp1[i][0], dp1[i][1])); } } } rrep(i, n){ for(auto x : G[i]){ if(x > i) continue; if(h[i] < h[x]){ chmax(dp2[x][0], dp2[i][1] + h[x] - h[i]); }else{ chmax(dp2[x][1], max(dp2[i][0], dp2[i][1])); } } } ll ans1 = max(dp1[n - 1][0], dp1[n - 1][1]), ans2 = max(dp2[0][0], dp2[0][1]); if(ans1 < 0){ out(-1); }else{ out(ans1); } if(ans2 < 0){ out(-1); }else{ out(ans2); } } int main(){ ios::sync_with_stdio(false); cin.tie(nullptr); input(); solve(); }